1. Field of the Invention
The present invention relates to a rolling bearing unit fitted with a rotational speed sensor (referred to hereunder as a speed sensing rolling bearing unit), used for rotatably supporting a vehicle wheel on a suspension unit, and detecting the rotational speed of the vehicle wheel.
2. Description of the Related Art
Referring to FIG. 8, there is shown an example of a speed sensing rolling bearing unit as disclosed in U.S. Pat. No. 4,907,445, for rotatably supporting a vehicle wheel on a suspension unit, and detecting the rotational speed of the wheel in order to control an anti-lock braking system (ABS) or a traction control system (TCS).
The speed sensing rolling bearing unit shown in FIG. 8, comprises a hub 3 having a flange 1 for wheel fixture provided on its axially outer end portion (hereunder axially outer end means the outer end in a widthwise direction when fitted to a vehicle; the left end in FIG. 8), and a first inner ring raceway 2a formed on an outer peripheral face of its axially central portion, and an inner ring member 4 externally fitted to the outer peripheral face of the central portion of the hub 3 and having a second inner ring raceway 2b formed on an outer peripheral face thereof. The inner ring member 4 constitutes an inner ring assembly together with the hub 3.
A threaded portion 5 is formed on an outer peripheral face of the axially inner end of the hub 3 (hereunder axially inner end means the end towards the center in a widthwise direction when fitted to a vehicle; the right end in FIG. 8), and a nut 6 is threaded onto the threaded portion 5 to thus press against the axially inner end face of the inner ring member 4, and thereby secure the inner ring member 4 at a predetermined location on the outer peripheral face of the hub 3.
An outer ring member 9 has an attachment portion 7 for attachment to a suspension unit (not shown), on an outer peripheral face thereof, and a double row outer ring raceway 8a, 8b is formed on an inner peripheral face thereof.
A plurality of rolling elements 10 are provided between the outer ring raceways 8a, 8b and the first and second inner ring raceways 2a, 2b, so that the hub 3 for wheel fixture is rotatably supported inside the outer ring member 9 supported on the suspension unit.
A cylindrical tone wheel 11 is externally secured to an axially inner half portion of the inner ring member 4. Recesses/protrusions 12 are formed on an axially inner end face (the end face on the widthwise inner side when fitted to a vehicle; the right end in FIG. 8) of the tone wheel 11, so that the magnetic characteristics of the inner end face are changed alternately in the circumferential direction and at an even spacing.
A cover 13 is fitted to an opening portion at the axially inner end of the outer ring member 9 to cover the opening of the outer ring member 9, and a sensor 14 is fixed to the cover 13, so that an axially outer end face of the sensor 14 is opposed to the recesses/protrusions 12.
A detection signal from the sensor 14 is taken out by means of a harness 15, and sent to a controller (not shown) for controlling an anti-lock braking system (ABS) or a traction control system (TCS).
At the time of operation of the speed sensing rolling bearing unit as described above, a vehicle wheel fixed to the flange 1 on the axially outer end portion of the hub 3 is rotatably supported relative to a suspension unit to which the outer ring member 9 is attached. When the tone wheel 11, externally secured to the inner ring member 4, rotates with rotation of the vehicle wheel, the output of the sensor 14 facing the recesses/protrusions 12 on the inner end face of the tone wheel 11 changes. Since the frequency with which the output of the sensor 14 changes is proportional to the rotational speed of the vehicle wheel, then if the output signal from the sensor 14 is input to a controller (not shown) by means of the harness 15, the rotational speed of the wheel can be obtained, so that an anti-lock braking system (ABS) or a traction control system (TCS) can be appropriately controlled.
The harness 15 associated with the abovementioned speed sensing rolling bearing unit can be up to more than 70 cm in length. This is because the speed sensing rolling bearing unit is mounted on the so-called spring foot portion on the wheel side of the suspension spring, whereas the mating member into which the connector on the end of the harness 15 is inserted is provided on the so-called spring head portion on the chassis side of the suspension spring. The harness 15 which must be long to cope with this situation, thus tends to hang down during shipping, and during installation of the speed sensing rolling bearing unit, interfering with the shipping and installation, and thus impairing the efficiency of these operations.
A construction has been adopted wherein, to avoid the drop in work efficiency due to the hanging harness, a connector is provided on the side of the speed sensing rolling bearing unit, and a plug on the end of the harness is inserted into the connector after completion of the installation.
However, when such a construction is adopted, the size of the speed sensing rolling bearing unit is increased due to the connector portion. There are thus cases where the above construction cannot be adopted, depending on the type of vehicle, because the installation space for the speed sensing rolling bearing unit is limited, or because the size increase for the connector portion is undesirable. Moreover, when the connector is connected on the wheel side of the suspension spring, which takes a considerable amount of vibration, there is the likelihood of a faulty electrical connection.